The long-term goal of the laboratory has been to obtain basic information about the molecular and cellular biology of corneal wound healing. During the current grant period, it was discovered that the two cellular components that specialize in sensing environmental changes, namely sensory neurons and antigen presenting dendritic cells (DCs), are functionally interdependent within the platform of corneal epithelium. Hyperglycemia drastically reduced corneal sensitivity and the density of sensory nerve fibers and endings in uninjured corneas, and significantly impaired re-innervation in post-wounding corneas. DCs, on the other hand, were found to co-localize with the nerve fiber innervating the epithelium and to ultimately contact with the nerve endings of the subbasal nerve plexus. Furthermore, in healing corneal epithelia, the number of DC cells was much reduced and the interconnections of DC with innervating nerve fibers/endings were disrupted in DM corneas, suggesting that DCs in these corneas have lost their ability to protect sensory nerves and to guide neuron regeneration post-wounding due to hyperglycemia. In addition to the DC-released neurotrophic factors, the wound-induced epithelium expression of nerve growth factor (NGF) was suppressed in DM CECs. Our published and preliminary studies led to the hypothesis that the altered interactions of CECs and DCs with sensory nerves result in diabetic neurotrophic keratopathy (DNK) and in delayed epithelial wound healing in diabetic corneas. The specific aims are: 1. To unravel the molecular characterization of DNK and its adverse effects on corneal epithelial integrity and intraepithelial dendritic cell function. This can be tested by measuring the relative density of sensory nerves and the contents of neuropeptides, and their correlation to epithelial signal transduction and to barrier function and to DC activation in NL versus DM corneas. 2. To determine the mechanisms by which dendritic cells guide epithelial innervation and post-wounding regeneration in NL corneas and their contributions to diabetic peripheral neuropathy (DPN). This can be tested by assessing the defects of DCs and CNTF and/or NT3 contents in diabetic corneas, and by delineating the functional requirements for sensory nerve innervation and regeneration in vivo and neurite growth in vitro in trigeminal neuron-DC co-culture. 3. To decipher how hyperglycemia disrupts epithelium-sensory nerve communication and causes delayed wound healing in the cornea. This can be tested by the epithelium-targeted expression of NGF, the blocking of NGF signaling in sensory innervation and regeneration in vivo, and neuron growth in vitro in trigeminal neuron-CEC-DC co-culture. The results from this proposal should increase our understanding of diabetic neurotrophic keratopathy and of delayed epithelial wound healing at the molecular and cellular levels, and should lead to the development of therapies that control diabetic neurotrophic keratopathy where there is an unmet clinical need.